Section 1

Editors Introduction

It's a Material World

Lynn Houghton

Journal Editor

In this journal we bring you material developments from Isola and Circuit Foil for High Speed and Automotive EV applications. Mark Goodwin calls for closer designer-supplier cooperation to ensure optimum material selection in this "performance hungry world".

We report on our third webinar with a ReCollect Soluboard update, latest developments in XRF metal thickness measurement and Dr David Shaw of A-Gas introduces us to economically produced, fully transparent flexible PCBs for enhanced LED signage applications.

Bill Wilkie covers the journey to our first online Foundation Course and check out Hans Vrijhof’s commitment and entertaining contribution in Industry News (Section 11)

From the youngest to the more mature, we mark the long service of our Council Member Maurice Hubert on his retirement. Thank you Maurice.

The ICT Journal is a public document and you are welcome to share it with your colleagues.

Go back to Contents

Section 2

Editorial

Recover to the New Normal

Paul Goodfellow, Minnitron Ltd, Ramsgate, UK

Paul Goodfellow
Managing Director,
Minnitron Ltd

Irrespective of your industry, your vocation or even your country it seems that our lives will be different from this day forward!

Many factors need to be addressed on a daily basis and some of the following questions may be relevant……

How resilient is our supply chain?
How can we use the current situation to benefit our company and therefore our customers?
Are we as a country too reliant on any given territory i.e China or Europe?
Can we shorten our supply chain to reduce the exposure to travel restrictions or more lockdowns imposed by the Corona Virus? 

It is more important than ever that companies seek out change. We can make changes to a number of key areas and I have used our experience at Minnitron as an example..

We are holding more stock of more difficult to source materials.
We are shoring up alliances with UK manufacturers that provide services that we can’t provide.
We have purchased a significant amount of good quality equipment to improve our in house manufacturing capabilities as well as quality.
We are broadening our product offering to provide a wider range based around our core competencies.

We are also looking even more closely at training for the already highly skilled and experienced staff as the investment in every individual pays huge dividends in product quality, consistency and of course the bottom line! I can never understand businesses that continually invest in their people but are unable to retain them! Staff and training thereof are huge costs and there is no point in training alone. If they aren’t happy for whatever reason, they simply won’t stay and then it is all a waste.

Minnitron Ltd has seen a lot of ups and downs in our 58 years of PCB manufacture. None quite like the COVID -19 pandemic but we have a proven track record in evolving through difficult times. I am happy to share these thoughts with you. We should all explore the opportunity in the chaos and make the best of this difficult time to once again thrive in moving forward.

Section 3

Calendar of Events

 Date

2021 Events

25th February

6th April - 27th May

1st June

7th September

November

AGM Webinar / Zoom Meeting

Webinar Foundation Course Lectures

Annual Symposium Webinar

Autumn Webinar

Evening Seminar and Facility Tour - Date to be confirmed

Go back to Contents

Section 4

New PCB material for demanding high temperature and high voltage requirements of the rapidly growing automotive EV market

Anna Graf and Michael J Gay, Isola Group

Anna Graf
Head of Application Engineering Europe/OEM Marketing Automotive,Isola Group

Michael J. Gay 
Director, High Performance Products, Isola Group

With the rise of automotive electrification, electronics system designers face significant challenges to achieve long-term, high reliability. The need for high voltage operation and fast charging coupled with reduced pitch and conductor spacing (miniaturization) requires the use of a material to enable designs for these extreme conditions. PCB’s will require a base material that has the capability to withstand electrochemical migration while operating in harsh environments at high voltage loads and extreme high temperatures.

In order to meet these major challenges Isola has developed a new material based on a unique resin technology. IS550H prepregs and laminates are glass reinforced, halogen free benzoxazine resin system materials, that still offer FR-4 processability combined with a thermal stability that go beyond an FR-4 High-Tg epoxy resin system and extreme CAF resistivity.

For electronic devices used in the electric power train of e-cars, for example, inverters and converters, where the requirements regarding thermal stability and high voltage CAF resistance are increasing. Operating temperatures up to 150°C are already requested. This may rise even up to 175°C when the new generation of semiconductors, like SiC, comes to use. These wide bandgap semiconductor materials will enable increased driving ranges and faster charging times. So the interest is high in the industry to push this technology. As operating temperatures up to 175°C are very challenging for FR-4 epoxy materials currently ceramics are options to meet this challenge. The main disadvantages of ceramics are the non-standard processability and high cost. That´s why Isola developed IS550H on basis of a benzoxazine resin to offer an organic, cost effective alternative to ceramics for these requirements to the market.

800V technology devices are already used in electric cars series production. Base materials used within this technology have to prove their high voltage CAF resistance up to 1000 V. With regards to the rapidly developing market also voltage ranges beyond 1000 V are considered.

Beside temperatures and voltages the operating time also becomes a critical factor. With a combustion engine vehicle the operation time is equal to the driving time. With an e-car the operation time is not only driving time but also charging time. This means that required testing cycles and hours have doubled or even tripled depending on the acceleration factor and test used. The standard 1000 cycles and 1000 hrs are no longer sufficient. 2000 cycles in TCT and up to 3000 hrs duration time in high voltage CAF test are today’s requirements.

IS550H has been extensively tested in regards of its suitability for all these demanding requirements. It passed 2000 hrs storage testing at 175°C with embedded copper coin TV´s and can be used for peak temperatures up to 200°C. It has shown an extremely high reliability and crack resistance when tested in thermal cycling test -40°C to 175°C for 2000 cycles. Beside these extreme thermal stability properties, it also has a significant improvement over FR-4 type materials with a thermal conductivity of 0.70 W/mK that enables embedded heat sink applications and an effective heat distribution within the material while heat losses are induced during operation. (Fig1)

Fig 1: Current Carrying Capacity test with 100 A, 200 A and 300 A performed on TV produced with IS550H and three other high Tg base materials

IS550H has demonstrated furthermore to achieve CAF performance at 1500V for 1000 hours for tight pitch, PTH to PTH and z-axis structures. (Fig 2 & 3) While it is not FR-4 material, IS550H’s processability is easy like common filled FR-4 materials.

Fig 2: 1000 V, 85 °C, 85 %RH, 1000 h CAF test; HW-HW distance 0.85 mm

Fig 3: 1500 V, 85 °C, 85 %RH, 1000 h CAF test; HW-HW distance 1.05 mm

Although IS550H was developed targeting electric vehicle applications, its extreme thermal stability makes it of course suitable for all thermally challenging devices like ie downhole drilling, avionics / military or engine management. Until now devices where thermal stability and reliability requirements go beyond epoxy FR-4 materials capability were realized with Polyimide base materials. With IS550H there is an excellent possibility to offer a material which can be used at higher temperatures compared to FR-4 and fills the properties gap to the Polyimide materials.

IS550H is available with core thicknesses ranging from 0.0020 inch (0.05 mm) to 0.063 inch (1.5 mm) and a wide range of prepreg resin contents for most applications including heavy copper designs. Please visit our website at www.isola-group.com for more information.

Section 5

Choosing the Right Materials is Tougher Than Ever

Mark Goodwin, Ventec International Group

The combination of rising performance expectations, intense commercial pressures and unexpected supply chain disruption means that choosing and getting hold of the right substrate materials for product designs is tougher today than it has ever been. As a wider selection of materials, with more finely nuanced properties, becomes available to designers, making the right choice is also increasingly complicated. Fortunately, help is available from suppliers and industry bodies. But designers can also help themselves by being more willing to share information with their suppliers.

Calling for closer working partnerships may be going against the grain in times of the global pandemic, as social distancing practices look set to continue to be an integral part of our daily lives. However, it is vital for us all to be more open from a technical standpoint if the next generations of high-tech products are to meet the world’s future needs. Complex, performance-hungry technologies like 5G and AI simply must succeed if we are to have the foundations necessary for smart living: smart energy, smart cities, smart buildings, smart factories, and smart healthcare are essential to ensure a high quality of life for all while preserving the planet’s resources.

As PCB industry veterans, we are well aware that the board is typically the last part of the project to be specified when a new product is being designed. On the other hand, it’s the first item to be needed when serious development begins. Designing the circuitry to go on the PCB obviously gets most of the attention, but the substrate itself is usually the lowest priority in engineers’ minds. When the time finally comes to consider it, teams will often simply default to using the same materials as were used previously. As the performance demands imposed on successive product generations continue to intensify, and factors such as conductive anodic filament (CAF) formation that seriously affect reliability become more critical, this approach is increasingly unsatisfactory.

As the industry has come to understand more about how the substrate properties influence performance and reliability under various operating conditions, so the number and diversity of material types on offer has increased. In the past there have been only a handful of options open to designers. Today, international specifications offer over 100 different material categories to choose from. Designers, understandably, struggle to connect the specifications with the properties they are looking for. It doesn’t help that these specifications are usually based on chemical composition. As the breadth of choice on offer continues to increase, it’s almost impossible for electronics engineers to relate to them. At Ventec, we have been calling for some time for the industry to move to performance-centric specifications that are easier for engineering communities to interpret.

Getting help is essential, because struggling on alone risks under-specifying or over-specifying the material for the application at hand. Neither is good: under-specifying risks the product coming up short in a way that could be beyond any realistic remedy. Over-specifying, to be “on the safe side”, can be commercially disastrous in ultra-competitive markets such as consumer technology. The chosen materials also need to be readily available in any location globally where the product is to be manufactured. Some resins, for example, are only available in certain domestic markets and are difficult to procure elsewhere.

So, what’s the solution? Qualifying or testing materials helps to understand their performance and properties but is expensive and time consuming for companies to undertake independently. Pooled testing, where groups of companies get together to do specific tests and share the results, is one response. There are a variety of industry initiatives that benefit from pan-industry participation that offer comprehensive sets of analyses that cover things like Dk and Df, CAF, thermal stress, and other tests on standardized test coupons.

Designers can also take advantage of another emerging trend among suppliers, which is to present carefully curated sets of materials for specific application areas. Our autolam and aerolam material guides (aerolam is launching this year), for example, bring together products with properties suitable for automotive or aerospace and further sub-divide them according to target applications and operating environments, such as under-the-hood or in-cabin. In this way, companies like Ventec effectively contribute their expertise to help customers shortlist products that can meet their requirements. This helps by simplifying and accelerating selection, narrowing the focus onto materials that are fundamentally suitable.

Helpful though this is, as suppliers we often need designers to express their requirements directly if we are to provide the right material for the right task. It’s of course understandable for any OEM to be wary of sharing information about their intellectual property and product strategies, but the value of trust between OEMs and their supply partners cannot be underestimated. As the issue of materials selection becomes more complex and, at the same time more important to get right first time, there is increasingly more to gain by finding ways to be open and more to lose by keeping traditional barriers in place.

 Section 6

Ultra Low Profile Copper Foil for Very Low Loss Material

Thomas Devahif,  Circuit Foil, Luxembourg

Thomas Devahif
R & D Engineer,
Circuit Foil, Luxembourg

ABSTRACT

Copper foil roughness has become a significant factor influencing conductor loss in high speed PCBs, particularly as they move above the 50 GHz range. At high frequencies, the current tends to flow mostly on the surface of the conductor (skin effect). When the so-called skin depth reaches the same dimensions as the roughness profile of the foil, the current follow its contour, inducing additional loss due to the longer propagation path. For regular very low profile copper foil, the roughness is around 3.0 µm (Rz ISO), meaning that the loss becomes significant at frequencies close to 1 GHz. To achieve good results over 50 GHz, the profile roughness must be well below 1.0 µm.

New ultra-low profile copper foils have been developed to achieve this property while maintaining a good adhesion with very low loss resins. Electrodeposited copper foil production is divided in two steps. First, the foil is plated on a titanium drum from a copper sulphate solution. Then a treatment is applied to increase roughness and ensure oxidation resistance. By using organic additives in the plating bath, the structure of the product can be controlled and the roughness decreased. Further improvement was achieved with titanium drums that had been polished with a specific grinding wheel to achieve a lower roughness on their surface. With a combination of both improvements, copper foils with roughness below 0.7 µm have been obtained.

The adhesion is usually increased with the treatment step by applying nodular copper particles. However, regular treatments have a significant impact on the roughness and therefore on the signal loss. A good compromise between adhesion and transmission properties was achieved with specific nodular deposits. For ultra-low loss application, a version of the foil without treatment has also been developed. Sufficient adhesion is ensured by silane-based coupling agent or organic coating.

Key words:
Copper foil, insertion loss, high frequency, low profile.

INTRODUCTION

Insertion loss
High frequency printed circuit boards applications have seen rapid growth during the last few years. Main driving factors are the combination of ever-increasing amount of information transferred on wireless networks with the widespread use of mobile devices. The emergence of radar sensors in the automotive sector, especially for the upcoming autonomous vehicles also requires electronic devices capable to carry high speed, high frequency signals with a limited size.
With frequencies above 50 GHz, the signal loss in a transmission line becomes significant. The total loss, or insertion loss, is the addition of conductor, dielectric, radiation and leakage losses [1,2]. The latter being associated with semiconductor materials, it is usually not taken into account for PCBs. Radiation loss is the energy dissipated in the surroundings of the conductor. It increases with the frequency and depends on the design of the circuit. Dielectric losses are linked to the substrate used in the PCB. For high frequency applications, low loss substrate with a dissipation factor (Df) in the order of 0.003 are commonly used [3]. The conductor loss depends on the nature of the transmission material and its surface morphology. It is the task of the copper foil manufacturer to provide products with the appropriate properties (at least on the side bonded to the prepreg) to minimize the conductor loss.

When an alternating current is going through a conductor, the changing magnetic fields induce the formation of additional electric fields (Eddy’s currents). Those fields are opposed to the “main” current in the centre of the conductor, but strengthen it on the outside (Figure 1.), resulting in an increased current density on the surface.

Figure 1. Formation of Eddy’s currents due to
changing magnetic fields in a conductor transporting AC.

This phenomenon, called skin effect, is stronger with higher frequencies. The effective section of the conductor where most of the current flows (the so-called skin depth) can be estimated with the equation below:

Where δ is the skin depth (m), f the frequency (Hz), µ the magnetic permeability (H.m^-1) and σ the electrical conductivity (S.m^-1) of the material (copper). The skin depth is a measure of the distance from the surface of the conductor at which the current density falls to 1/e of its value on the surface [4]. Around 98% of the current flow at distance of four times the skin depth. It is below the micrometre range for frequencies over 4 GHz (Table 1.).

Skin effect has two impacts on the conductor loss. Firstly, the effective cross-section of the conductor carrying the current is reduced, inducing a higher AC resistance. Secondly, for conductors with a rough profile, a low skin depth will cause the current to follow the contour of the material, increasing the effective length of the propagation path (Figure 2.). It has been demonstrated that surface roughness can double the conductor loss [5].

Figure 2. Comparison of current flow for DC and high frequency AC
in a rough copper foil.

To mitigate this effect, copper foil manufacturers must develop new profile-free products. For regular copper foils, the roughness is voluntarily increased to improve the adhesion. It is considered that over 90% of the peel strength between a rough copper foil and a prepreg is due to mechanical forces, while the remaining peel strength is due to chemical adhesion. On a low or no-profile copper foil, the mechanical strength is drastically reduced.

IPC-4562 defines 3 major classes for roughness profiles, irrespective of the foil’s thickness (Figure 3.). Below 5.1 µm (200 µinch) is defined as “very low profile”. However, this definition is behind the industrial progress. Latest low roughness copper foils are usually named as “HVLP” (Hyper Very Low Profile Copper), with incremental numbers for each new generation. HVLP would have a roughness below 3.0 µm Rz ISO, HVLP2-3 below 1.3 µm and HVLP4-5 below 0.9 µm. The distinction between HVLP 2/3 and 4/5 is related to the type of treatment applied, not so much impacting Rz values but rather more accurate parameters such as 3D measured surface developed ratio. Another gap is found among definitions of Rz since Rz ISO is not identical to Rz JIS. For very low roughness, this difference is significant and can be above 25%.

Figure 3. Grades of copper foils roughness [6]

This paper discusses the development of HVLP 2 to 5 copper foils with a roughness below 1.0 µm in Rz JIS, i.e. 1.3 µm (50 µm inch) in Rz ISO (all the roughness data presented below are expressed in Rz ISO).

Electrodeposited copper foil manufacturing
Electrodeposited (ED) copper foil are produced in two steps. Bare copper is first deposited on rotating titanium drums (cathode) to form a continuous film (plating step). The parameters of the foil can be adjusted depending on the plating conditions. Unlike rolled annealed foils, the process is assymetrical and ED copper foils have two different sides: the drum side was in direct contact with the cathode and its structure is the negative copy of the drum surface. The electrolyte side was in contact with the solution. Its roughness can be controlled with organic additives impacting copper deposition process.

The second step of copper foil manufacturing is the treatment. Several electro-chemical processes improve the foil adhesion and ensure oxidation resistance. Firstly, copper nodules are deposited on the foil to increase its surface area and therefore the adhesion. To obtain this, specific electrolysis conditions must be used: low copper concentration with high current density (Figure 4.).

Figure 4. Copper deposit structure depending on electrolysis parameters
(where J / C _Me^Z+ is the current density and inhibition density is copper concentration,
temperature or the presence of additives) [7]

Zinc and chromate passivation layer is subsequently deposited to provide oxidation and thermal resistance. Chemical adhesion is guaranteed by a silane coupling agent.

Roughness Measurement
The roughness of copper foils is usually measured with a contact profilometer: a stylus follows the surface to recreate a linear profile from which the Rz can be calculated. However, this contact method may not be appropriate for low roughness foils with fine treatment nodules. A comparison with white light interferometry measurements will be made in this paper.

DEVELOPMENT OF ULTRA LOW PROFILE COPPER FOIL

Background
The physical parameters of an ED copper foil can be controlled with the addition of organic additives into the plating bath. Certain additives – known as levellers – can decrease the roughness of the surface. During the electrodeposition process, the current density and electric field strength are higher on the peaks of the substrate which therefore tend to grow faster. This yields a rough surface. However, some organic molecules are adsorbed preferentially on the peaks of a surface and can locally inhibit copper growth, favouring deposition on the valleys. The result is a product with a much smoother profile (Figure 5.).

Figure 5. Copper deposition with and without organic additives (levellers) [8].

The roughness of foils produced only with levellers falls into the range of “low profile” product (4-6 µm for 35 µm (1 oz./ft²) thick foil). HVLP foils are produced by combining levellers and other types of organic additives called brightners that can give the electrolyte side of the foil a smooth and shiny aspect (Figure 6.). The roughness of those HVLP foils is around 1.9 µm (Table 3.).

Figure 6. SEM imaging of 35µm (1 oz./ft²) base copper foil prior treatment:
(1) low profile foil; (2) HVLP; (3) HVLP2/3; (4) HVLP4/5

Production of ultra low profile foils
To reduce the roughness below 1.3 µm, several improvements of the plating process were made. The most obvious way is to change the organic additives for more effective ones. This can easily be tested in the laboratory. Copper deposition is made in a large beaker with solution parameters as close as possible to the production bath. The results can never exactly be the same as than on the line, but the trends are very informative. Several additives have been compared in the laboratory (Table 4.). It appears that the roughness of ultra-low profile foil can be decreased significantly with an improved additive.

.
The second improvement is linked to the titanium drum on which the copper foil is plated. Its surface impacts directly the copper foil drum side morphology, but also to some extent the electrolyte side. Indeed, for very low thicknesses such as 9 and 12 µm (1/4 and 1/3 oz./ft²) there is a correlation between drum side and electrolyte side roughness (Figure 7.).

Figure 7. Impact of drum side roughness on electrolyte side
for low thickness HVLP foil (9 µm).

With a specific preparation method, the drum surface roughness could be decreased down to 1.25 µm. The impact on electrolyte side roughness is estimated to be in the 0.1 to 0.2 µm range. Long term production runs have highlighted that the polishing done after each roll to remove the oxidation on the drum’s titanium surface had little to no impact on its roughness (Figure 8.).

Figure 8. Evolution of drum side Rz during one month of production
on low roughness drum (each measurement was
done after a polish of the drum surface).

With both additives and drum surface improvements, the roughness could be decreased well below 1.0 µm for all thicknesses (9, 12, 18 and 35 µm). Those improvements are reflected in the insertion loss measurements (Table 5.). HVLP3 and 4 foils have significantly improved electrical performances compared to first generation HVLP. From a mechanical point of view, ultra-low profile foils behave like any regular low profile copper foil.

TREATMENT OF ULTRA LOW PROFILE COPPER FOIL

Background
Copper foil treatment improves both adhesion and oxidation resistance. Standard non metallic passivations are considered to have little to no effect on the insertion loss. Indeed, the layers are extremely thin (around 3 nm on treated side and 10 nm on untreated side which are etched away in the PCB manufacturing process) and mostly nonconductive. However, the nodular copper particles applied to improve the adhesion can impact significantly the insertion loss due to their conductivity and the increased roughness. On regular ED copper foils, the nodule size is around 5 µm.

Ultra-low profile nodular treatment
Nodular treatment is essential on copper foils to ensure sufficient adhesion. For low loss applications, a compromise must be found between insertion loss and peel strength on low loss materials (the target is usually > 2.8 pli or > 0.5 N/mm). New ultra-low profile nodular treatments were therefore developed specifically for HVLP2, 3 and 4 foils.

Low profile nodular treatment applied on HVLP foils is a uniform layer of round-shaped nodules covering the surface (Figure 9.). With a nodule size around one micron, it ensure excellent adhesion and thermal resistance at the expense of a significant increase of roughness compared to the base foil (+ 0.5-0.7 µm of Rz ISO). HVLP2 benefits from a lower roughness base foil, but also a treatment with a 5 fold nodule size decrease compared to HVLP. It offers a good compromise between adhesion and electrical performances.

Figure 9. SEM pictures of (1) HVLP, (2) HVLP2, (3) HVLP3,
(4) HVLP4, (5) HVLP5 profile free copper foils

As further decrease of treatment size would result in insufficient peel strength, a different methodology was followed for HVLP3 foil. In this case, the use of specific silane based adhesion promoters in combination with appropriate surface finish greatly increased the contribution of chemical adhesion, allowing further treatment size reduction (20 times smaller than HVLP2). For HVLP 3 or 4 type foil, we estimate that mechanical adhesion accounts for only 50 % of total adhesion, instead of more than 90 % for previous generations copper foils. Interestingly, when comparing HVLP 3 and 4 whose only difference is the base foil roughness, HVLP4 tends to have higher peel strength. It is assumed that the smoother surface allows for a more homogenous treatment deposition, improving its properties.

On HVLP5, the fine tuning of passivation chemistry and the use of high adhesion silane coupling agent allowed to reach good peel strength on most low loss materials with a nodular free copper foil. However, silane type may have to be changed depending on the targeted resin system in order to ensure optimal adhesion.

Passivation
The HVLP copper foils are passivated with a non metallic layer ensuring high stability of the laminate at temperatures up to 280°C for one hour. For low loss applications, this passivation is expected to exhibit better performances than Nickel or Cobalt based treatments for example. Indeed, due to its lower conductivity than Copper, a thin layer of Nickel can impact significantly the signal loss at high frequency [9]. This has been verified by applying a Nickel passivation layer on nodule free foil and comparing the insertion loss with the one of the regular product (Table 7.). The Nickel layer slightly improves the adhesion but also impacts the signal loss. However, it helps to improve the thermal resistance of the foil. For applications where a high thermal resistance is required, all HVLP products are available with a “HT” Nickel-containing passivation.

ROUGHNESS MEASUREMENT
The roughness of copper foils is usually measured with a contact profilometer consisting of a diamond needle (stylus) sliding on the surface. This method is appropriate for high roughness copper foils, but shows limitations for the ultra-low profile products. Indeed, it cannot detect the additional roughness caused by the treatment since the nodules size is smaller than the needle tip (< 1 µm). The profilometer is clearly scraping through the treatment, only taking into account the base foil roughness (Figure 10.). This is the reason why nearly no difference in roughness could be seen between the base and treated foils for HVLP 2 and 3 grades, or for HVLP 4 and 5.

Figure 10. SEM picture of the trace left by the stylus used
for roughness measurement on HVLP2 foil.

A more appropriate surface roughness measurement for ultra-low profile foils is the white-light scanning interferometry. The principle is to divide a light beam in two paths, directing one to a reference mirror and the other one to the sample surface. This measurement beam travel different distances depending on the surface profile. The two waveforms are then recombined and create interference patterns depending on their phase difference. Those patterns are analysed to calculate the height of the sample at each point (pixel) scanned [10]. Unlike the stylus method, light interferometry does not damage the sample and can measure height differences smaller than 0.1 µm. 3D roughness are expressed as “S” parameters such as Sa or Sz.

Depending on the parameter, different information about the surface profile will be available. For example, Sz value which is the height difference between higher an lowest point on the surface is much less sensitive to the treatment size as it is usually smaller than the roughness range (waviness) of the base foil. It can be correlated to some extent with the Rz measured with a profilometer. Sa which is the arithmetic mean deviation won’t be greatly impacted by latest generation treatment (HVLP3/4) either. The sdr – defined as the ratio between the developed surface and a perfectly flat one having the same dimension – is however very sensitive to the nodular treatment size and surface area, parameters which are critical for insertion loss properties. Therefore, we consider Rz, Sz and Sa to be macroroughness parameters more related to base foil roughness for ultra-low profile copper foils, while sdr is a microroughness measurement.

CONCLUSION
Ultra-low profile copper foils have been developed with both plating and treatment improvement. The use of specific additives and low roughness drums for the base foil production resulted in a decrease of roughness down to 0.7 µm. Sufficient adhesion (0.5 N/mm) was obtained with a very low profile nodular treatment or no treatment at all to minimize impact on both roughness and insertion loss.

The use of white-light scanning interferometry ensured an accurate measurement of the foil’s roughness, even for the smallest treatment features.

FUTURE WORK
Future development will focus on further reduction of the base foil roughness and the improvement of the adhesion of the no profile copper foil. New approaches are being tested regarding the plating conditions of the base foil in order to further reduce the roughness, especially for the low thickness products. The influence of current density, copper concentration and leveller nature are being further evaluated. The most challenging yet important project remains nonetheless the adhesion of no profile foil. New chemical adhesion promoter must be found in order to ensure a peel strength well above 3.0 pli on a broad range of resin systems without roughness increase. Another alternative would be to deposit a rough yet non-conductive layer on the smooth copper surface to ensure adhesion with minimal insertion loss.

REFERENCES
[1] J. Coonrod, “Insertion Loss Comparisons of Common High Frequency PCB Constructions”, IPC APEX Conference Proceedings, February 2013.
[2] J. Coonrod, “Understanding PCBs for High-Frequency Applications”, Printed Circuit Design & Fabrication: Circuits Assembly, October 2011, Vol. 28, Issue 10, p. 25.
[3] J. Coonrod, “Selecting PCB Materials for High-Frequency Applications”, Microwave Engineering Europe, March 2012, p. 18-21
[4] G. Brist, S. Hall, S. Clouster, T. Liang, “Non-Classical Conductor Losses due to Copper Foil Roughness and Treatment”, Electronic Circuits World Convention Proceedings, 2005, vol. 10, p. 22-24.
[5] A. Horn, J. Reynolds, P. LaFrance, “Effect of conductor profile on the insertion loss, phase constant, and dispersion in thin high frequency transmission lines”, DeignCon 2010.
[6] J. Mouzon, J. Petry, L. Vast, “Ultra-flat and almost no profile ED-copper foils for high speed digital PCBs”, PCB Magazine, March 2014, p. 68-76.
[7] R. Winand, “Electrocristallisation. Théorie et applications.” Journal de Physique IV Colloque, 1994, p. C1-55-C1-73.
[8] A. Wolski, “Electrodeposited copper foil for printed circuits”, Foil Technology Development Corporation, 1998.
[9] D. Cullen, B. Kline, G; Moderhock, L. Gatewood, “Effects of surface finish on high frequency signal loss using various substrate materials”, CIRCUITREE-CAMPBELL-, 2001, vol. 14, p. 80-80.
[10] J. Marshall, “Measuring Copper Surface Roughness for High Speed Applications”, IPC Proceedings, 2015.

Section 7

ICT Webinar Review June 1st 2021

Recyclable PCBs, and More

Pete Starkey, I-Connect007

Another excellent technical webinar on June 1, introduced and moderated by ICT Chair Emma Hudson, provided updates on developments in recyclable PCBs, innovations in transparent flexible displays, and X-ray fluorescence techniques for the determination of the thickness and composition of metal coatings.

“It is time for us to take responsibility for our electronics and the impacts that they are having on the planet,” said Jack Herring, CEO of Jiva Materials, who reported the progress of the ReCollect project for recyclable PCBs.

Recyclable PCBs

Commenting that 32% of all e-waste consisted of small domestic equipment and that current recycling techniques for the recovery of precious metals such as gold, silver, and palladium involved shredding and incineration, he explained that the focus of the ReCollect (Recyclable Composite Laminates for Electrical Goods) project was to develop an alternative way of managing end-of-life circuit boards by removing difficult-to-recycle fibreglass-epoxy PCBs from the supply chain. Primary objective was to demonstrate the feasibility of producing a PCB substrate in high volumes within the UK, with performance comparable to CEM1 and FR-4, with circuits formed by additive or subtractive techniques. An important secondary objective was to ensure its compatibility with existing aqueous fabrication processes.

Target market was the white goods and domestic appliance sector, including dishwashers, fridges, and washing machines, the manufacturers of which already had well-established recovery schemes in place, enabling PCBs made on the new substrate to be removed and recycled. Jiva’s patented solution was a flame-retardant composite of natural fibres and a polymer resin that dissolved in hot water yielding non-toxic and biodegradable by-products, avoiding energy-intensive recycling by shredding and incineration and enabling substantially higher yields in precious metal recovery. Herring estimated the soluble PCB to have 60% lower carbon footprint than the equivalent FR-4 product and a plastic saving equivalent to 620 grams per square metre. Indeed, if used in just 1% of European domestic appliances, 100 tons of plastic could be eradicated.

Small quantities of PCBs had been produced in Jiva’s UK development laboratory and the recycling process was being developed to establish a take-back scheme for end-of-life electronics and enable customers to benefit from an effectively circular supply chain.

Herring showed examples of single- and double-sided printed electronics on unclad substrate, assembled using conductive silver epoxy, with low-temperature soldering in development. Copper-clad laminates had been manufactured, and mechanical drilling and routing parameters had been established. Etching had been successfully demonstrated and processes for through-hole connectivity were being explored. The substrate was thermoplastic and potentially mouldable into three-dimensional profiles.

An extensive third-party testing programme was nearing completion, and had shown mechanical properties to be comparable to CEM1 and electrical properties comparable to CEM1 and FR-4. Flame retardancy was in line with UL 94 V-0, and it was planned to submit samples for formal UL classification in Q4 2021. The material had attracted interest from white-goods, LED lighting, and computer-peripherals industries.

View slides here.....ReCollect_ICT_Summer_Webinar.pdf

Transparent Flexible Lighting

The topic of the second presentation was developments and innovations in transparent flexible lighting, delivered by Dr. David Shaw, business manager for semiconductor technologies at A-Gas Electronic Materials. He explained that although indium tin oxide had become established as the industry standard transparent conductive film and would continue to be dominant on glass substrates, it had limited capability for flexible applications. It was not formable or stretchable, it was not as transparent or as conductive on plastic as on glass, and circuit patterns were costly to create.

Alternative materials included conductive polymers such as PEDOT, silver nanowires, and copper or graphene micromeshes, none of which could fully satisfy the combined needs for transparency, conductivity, affordability, environmental stability, flexibility and formability.

A carbon nanotube—silver nanowire hybrid material had now been developed which not only met these requirements but could also be cost-effectively patterned by basic technologies without the need for high-resolution laser ablation. A flexible film, roll-to-roll coated with a silver nanowire dispersion, was screen-printed with a conductor pattern using a carbon nanotube ink, after which the exposed silver nanowire areas were removed with a mild ferric nitrate etchant to create a patterned transparent conductive film. A range of sheet resistances from 10 to 75 ohms per square could be achieved. If copper micromesh materials were used, sheet resistance could be reduced to 1 ohm per square.

Application areas included transparent heaters, transparent antennas, transparent lighting films and transparent touch sensors, and there were enormous growth opportunities in automotive, transparent LED and digital signage market segments.

View slides here....A Gas presentation June 2021.pdf

X-ray Fluorescence Techniques

With the proliferation of thin metallic final finishes for soldering and wire bonding: ENIG, ENEPIG, EPAG, RAIG, IGEPIG, DIG, and so on, accurate thickness measurement has always been a challenge. It must be fast, precise, non-destructive and cost effective. The IPC-4552A performance specification for ENIG refers to X-ray fluorescence methods, making some recommendations regarding instrumentation, discussing verification of the measurement process and assessing its capability.

In the final presentation, Zach Dismukes, global product manager with Bowman Analytics, reviewed new developments in X-ray fluorescence techniques to enhance throughput and precision in ENIG and ENEPIG measurement.

He began with an enlightening introduction to the principles of X-ray fluorescence, without venturing too deeply into the theoretical physics, describing how X-rays interacted with inner-shell electrons to cause some to be ejected and be replaced by electrons from higher orbitals, filling the holes left behind. The energy difference of electrons moving between orbitals was released in the form of photons with a specific wavelength characteristic of the element. Thus X-ray fluorescence related to the absorption of radiation of a specific energy, resulting in the re-emission of radiation of a different energy. This gave the basis of a spectroscopic analytical method for measuring elemental composition and plating thickness. In principle, the method was applicable to all metallic elements from aluminium to uranium, at thicknesses from sub-nanometre to microns, and could measure thickness and composition simultaneously, up to five layers and 25 elements.

Recent developments in X-ray fluorescence spectroscopy gave improved stability and enabled the statistical capability requirements of IPC-4552A to be met with a shorter measurement time. Dismukes explained the advantages of large-window silicon drift detector technology, and polycapillary optics for optimised focusing of x-ray beams. He also discussed the characteristics of different tube targets and described some of the advanced software-automation features now available, such as autofocus, pattern recognition, XYZ programming, and fully-customisable data-export for automatic generation of reports.

View slides here.... Bowman Analytics Presentation.pdf

After moderating a Q&A session, Emma Hudson thanked all participants and particularly acknowledged ICT technical director Bill Wilkie’s smooth organisation of the event. Although ICT’s series of technical webinars had been extremely successful, she was hopeful that there could soon be a return to live seminars and symposia with all of their networking benefits.

Published by kind permission of Pete Starkey, I-Connect007

The Webinar can be viewed on the ICT You Tube Channel here

Section 8

Foundation Course

Annual Foundation Course 2021

Bill Wilkie, ICT

Bill Wilkie
Technical Director and Membership Secretary, Institute of Circuit Technology

This year’s Annual Foundation Course has been unlike anything in it’s history, starting in 1980 in Galashiels College of Further Education. Moving swiftly to Heriot Watt campus and then through Loughborough University and eventually Chester University, it began as a two week residential course and transformed with the PCB Industry into a tight course over four and a half days.

The first day was sponsored by Merlin at their Deeside plant so we could take in a facility tour, a staple part of the event going right back to the start of the course

With the UK’s universities closed to all events due to covid, an idea was born and began to emerge last Autumn. Lecturers were sounded out and a schedule put in place for Tuesdays and Thursdays every week during April and May. Member companies who had sent delegates in the past were canvassed and then we distributed the idea in a mail shot to all our members.

We had a crash course in meeting platforms in the Autumn and signed up for Zoom – no going back.
We had no real idea how many delegates we would attract, but in the end we had bumper input, with 40 registrations, although not all were able to sit in on every lecture. We enrolled 35 new Associate Members, since this course satisfies one of the council’s criteria for Membership.
It was never going to be smooth, but we didn’t anticipate emails going astray and lecturers pulling out at the last moment. A rolling fortnightly system of informing delegates and lecturers was set up, with trial runs for any of them not familiar with Zoom. This cast up poor bandwith in some areas and we had a lecturer sent home early to run the webinar from home, where the broadband was better.
We went almost to the end before discovering that a headset delivered a much better performance!
With our zoom Diary empty, the printer was kept busy ensuring that delegates were able to receive Attendance and Membership Certificates, each with its own ICT waxed seal.
Members joining the Institute are logged onto our website and receive a welcome email, with password and instructions and that’s it till next year. Back to Chester or will it be a Zoom call – crystal ball anyone?

Thanks also to the following who attended the lecture hours, which were job specific.

Amphenol-Invotec
Lee Parr
Mark Vernon
Mike Timmins
Mark Mills
Martin Williams

Holders Technology
Kelvin Scott

Sun Chemicals
Erika Rebrosova

Section 9

PCB Fabricators Group - a Benefit to all who Fabricate PCB’s in the UK. 

Matthew Beadel
Technical Director,
Merlin Circuit Technology

The fabricators group met for its 2nd meeting of 2021 and again the turnout was high – a trend that we hope will continue for the future.

 The meeting was ‘as ever’ very interesting and again lasted the 2 hours as there was plenty to discuss. Some of the topics of discussion centred around both Covid (mainly restrictions of service engineers from Europe and USA) and the aftermath of Brexit (which is still being felt). The group as a whole believed that the UK PCB industry was ‘heading in the right direction’ even though there’s been many bumps in the road. There was however concerns over supply of laminate and the various increases in material cost and very extended leadtimes that have been imposed on the Fabricators by many (although not all) suppliers. Copper foil supply was also discussed as a potential issue with the increase in requirement for Electric cars, although not something that has been felt too severely in the UK yet – the following months will be telling!

As always we are very happy to welcome new members to the group, please let either Bill Wilkie know or contact the Fabricators group directly.

Go back to Contents

Section 10

Industry News 

Title

King's Day

Converting a long running, one-week Annual Course into a 16-week lecture series was never going to be without problems. We were able to resolve issues of missing emails, quantify the struggle with bandwidth and broadband speeds, but when it came to last minute replacements for lecturers, we were almost stumped.

It was at the eleventh hour that we managed to track down a MacDermid Alpha representative from the Netherlands, called Hans Vrijhof, who mailed that he might be able to do something similar to the ‘Etching and pre-treatment’ Lecture.

He subsequently gave me a call and I discovered that this stalwart was actually on a public holiday, called King’s Day and would have to forswear all drink until he completed the presentation. I quickly found out that the King’s Day celebration is held every year on the 27th April, with revellers dressing in orange costumes and generally having a good time.

The Royal Family on Koningsdag

Our thanks to Hans Vrijhof of MacDermid Alpha for stepping in at the last minute and also supplying these pictures of King’s Day.

UL Approval for Halogen Free Laminate

CC Electronics is proud to have been approved for Halogen Free laminate.

If you have any feedback or questions about Halogen Free Laminates or would like to request a quote

Simply get in touch by emailing This email address is being protected from spambots. You need JavaScript enabled to view it.

Alan Green, GM at Lyncolec: 54 Years In The Making!

Lyncolec Ltd. are quietly celebrating something quite monumental. Alan Green is our General Manager and he is celebrating 54 YEARS cumulative experience in the Printed Circuit Board (PCB) industry!

Alan has worked with many prestigious PCB manufacturers since 1967, and has witnessed first-hand the evolution of the industry and products which accompany it. Let's put that into context...Read more...

Merlin Circuit Technology Ltd Laser Drilling and Stacked Via Technology

Merlin has recently increased its technical capability with the introduction of laser drilling and stacked via processes. This has been achieved with the financial assistance of SMART CYMRU and the European Regional development fund. This technology complements the other high technology processes already being offered by Merlin Circuit Technology at its facility in North Wales. Read more.... 

Members News

 Maurice Hubert

Some of the Succesful Participants of the Foundation Course 2021

Lisa Trust, Production Control, raises over £1000 for Cancer Research UK

With lockdown in 2020, being furloughed and COVID hitting everyone’s mental state of mind I needed something to give me a boost. After Christmas a challenge to run 56 miles in February 2021 for Cancer Research, popped up on Facebook. This seemed like the perfect way to clear my head and help out a great charity, I hadn’t run for almost 2 years due to various injuries so it was always going to be a challenge not only the finish 56 miles but to not pick up another injury. A group of us at Exception have completed a few charity walks, we did the 3 peaks for Birmingham Children Hospital in 2018 and 5 Valleys Walk in 2019 for Meningitis.

Section 12

Membership News 

12.1

 Membership Update

NEW MEMBERS SUMMARY Mar-Jun 2021

Hannes Hunger

RUAG

Bill Wilkie
Technical Director and Membership Secretary, Institute of Circuit Technology

 Section 13

Corporate Members of The Institute of Circuit Technology

Section 14

ICT Council Members

Council Members

Emma Hudson (Chair), Andy Cobley (Past Chairman), Steve Payne (Deputy Chairman), Chris Wall (Treasurer), William Wilkie (Technical Director, Membership & Events), Richard Wood-Roe (Web Site), Lynn Houghton (Hon Editor), Matthew Beadell, Martin Goosey, Maurice Hubert, Lawson Lightfoot, Peter Starkey, Francesca Stern and Bob Willis, 

Go back to Contents

Section 15

Editors Notes

The ICT Journal

Lynn Houghton
Journal Editor

Instructions / Hints for Contributors

1. As it is a digital format the length is not an issue. Short is better than none at all!

2. Article can be a paper or a text version of a seminar or company presentation. Please include data tables, graphs, or powerpoint slides.We can shrink them down to about quarter of a page. Obviously not just bullet points to speak from.

3. Photo's are welcome.

4. We would not need  source cross references

5. Title of presentation - Of course! Date, Job title of Author and Company represented.

6. An introductory summary of about 150 words would give the reader a flavour of what it's all about.

7. Style - we don't want out and out advertising but we do recognise that the speaker has a specialism in the product or process that will include some trade promotion. Sometimes it will be a unique process or equipment so trade specific must be allowed.

8. Date and any info relating to where or if this article may have been published before.

9. We can accept virtually any format. Word, Powerpoint, publisher, PDF or Open Office equivalents. 

10. Also, to make it easy, the author can provide a word file to go along with his original powerpoint presentation and I/we can merge it together and select the required images. 

11. A photo of author or collaborators.

I really do look forward to receiving articles for publication.

Lynn Houghton

This email address is being protected from spambots. You need JavaScript enabled to view it.

Go back to Contents